The invention relates to water systems. More particularly, the invention relates to high purity water systems for laboratory, medical, industrial, and similar uses.
An exemplary high purity water distribution system delivers water to a number of delivery or use points. One exemplary delivery/use point is a faucet. Another exemplary delivery/use point is a water-utilizing piece of laboratory, medical, or industrial equipment.
Despite initial purification, high purity water systems have contaminant growth problems. Stagnant water in a system may provide a hospitable location for any residual contaminant to grow to unacceptable concentration. For example, a typical laboratory faucet is fed by a branch off of a main distribution line. When the faucet is shut-off, there may be stagnant water in the branch even if there is constant flow through the main distribution line. For example, constant flow through the main distribution line may be achieved by providing the main distribution line as a recirculating system.
FIG. 1 shows a “serpentine” system 20 having an initial non-purified water supply 22 (e.g., municipal water or main water for an industrial facility). A purification system 24 may include: one or more filters 26; thermal, or radiological processing stations 28; and pumps 30. The purification system 24 delivers purified water to a purified water reservoir 40 (e.g., a holding tank). An exemplary main distribution line 42 is a recirculating line from an outlet 44 of the tank 40 to a return 46 of the tank 40. A pump 48 may be located along the main distribution line 42. The distribution line 42 may serpentine through various locations in the laboratory to deliver purified water to various distribution/use points 50.
An exemplary distribution/use point is a faucet 52 having an outlet 54 and a valve 56. The faucet may be at the end of a branch line 58 from the leg of a tee 60 along the distribution line 42. In the exemplary faucet, the branch line 58 connects to a port 62 of the faucet. The exemplary port 62 and valve 56 are along a faucet mounting base 64. Depending upon faucet geometry, at least the distance from the tee 60 to the valve 56 may constitute a dead leg wherein there is little water circulation when the faucet is shut-off. To limit dead leg contaminant growth, one possibility is to leave a residual flow through the faucet. For example, the faucet may have a nominal shut-off condition in which a small flow is discharged (e.g., to waste). Also, or alternatively, limitations may be placed upon the length of the dead leg. For example, with a very short dead leg, residual communication at the tee 60 between the branch line 58 and the main distribution line 42 may sufficiently limit stagnation in the dead leg.
Recent design practices dictate that a dead leg in a hot water system, should not exceed a length greater than six pipe diameters; in a cold system it is any static area, although rule of thumb numbers of three or four diameters are commonly used. This length is often referred to as the “6d” rule and has traditionally been determined by measuring the distance from the centerline of the supplying conduit to the physical blockage on its associated branch. See, e.g., Genova T F, “Microbiological Aspects of Pharmaceutical Water Systems,” presented at the High Purity Water Seminar, Institute for International Research, Westin Resort, Miami Beach, Fla., February 1998. Some less conservative gooseneck faucet configurations violate this rule.
An alternative system involves the use of recirculating laboratory faucets (RLFs). FIG. 2 shows a “supply/return” system 20′ wherein the distribution line 42′ is divided by a balancing valve 43 into a supply/outbound leg/line 42-1 and a return/inbound leg/line 42-2. The balancing valve 43 maintains a pressure in the outbound line 42-1 above a pressure in the return line 42-2. In each use point 50′, the faucet 52′ has a supply port 62-1 and a return port 62-2. The supply port 62-1 is connected to the supply line 42-1 via a line 58-1 and a tee 60-1. The return port 62-2 is connected to the return line 42-2 via a line 58-2 and a tee 60-2. The faucet 52′ has an outlet 54′ and a valve 56′. With the valve 56′ shut-off, there is no discharge flow from the outlet 54′. However, there is a recirculating flow along a recirculating flowpath (faucet loop) 70 from the tee 60-1 through the line 58-1, port 62-1, port 62-2, line 58-2, and tee 60-2 to return to the return line 42-2 and therefrom to the holding tank. By providing this residual recirculating flow, the dead leg may be substantially internalized to the faucet (and reduced to essentially zero with a purpose-configured RLF). This provides a great deal of flexibility in locating the faucet relatively remote of the supply line and return line. When the faucet 52′ is open and flow discharging from the outlet 54′, there may still be a residual return flow through the line 58-2.